1. Field of the Invention
The present invention relates to a band for a centrifuge rotor, and in particular, to a band configured such that, in operation, it is subjected only to tensile forces.
2. Description of the Prior Art
The manufacture of rotating structures, such as centrifuge rotors and energy storage flywheels, has evolved from the use of homogeneous materials, such as aluminum and titanium, toward the use of composite materials. The use of such materials is believed advantageous because it permits the attainment of increased centrifugal load carrying capability. The increased load carrying capability is achieved because the lighter weight of the composite rotor permits it to spin faster for a given motive input, thus resulting in a greater relative centrifugal force.
The rotating structures of the prior art believed relevant to the present invention each have some form of band that, while at rest, exhibits a predetermined arbitrary shape. However, such a band is subjected during operation to a load due to the tendency of the band to change from the arbitrary rest shape to some equilibrium rotating shape. This phenomenon may be understood from the following simplified example.
Consider an applied load accepting band for a centrifuge rotor that in the rest (i.e., non-spinning) condition is circular in shape. Assume that this band accepts three applied loads corresponding to three equiangularly spaced sample carriers. When such a rotor is spun the effects of centrifugal force on the sample carriers apply loads that act radially outward, tending to pull the band to form "corners". The perimeter of the band generally intermediate the applied loads will thus deflect radially inwardly from their original circular shape. Since the band has some predetermined stiffness associated with it, the deflection of the band from its rest shape to its equilibrium shape while rotating imposes a bending stress on the band. This bending stress in the band does not contribute to its load carrying capability, and in fact, is deleterious to the band since it results in reduced rotor life.
In view of the foregoing it is believed advantageous to provide a centrifuge rotor which is not exposed to the stresses associated with the change in shape as the band is spun, thus avoiding the deleterious effects attendant therewith.